Harpies

The Harpies are the secondary antagonists of the series; first introduced as interceptor type, ambush-class angeloids type gamma, they were manufactured as 1st generation angeloids. Their roles as secondary antagonists (next to the Master of Synapse) answers directly to the Man of Synapse, and they serve as the guards to the entrance of synapse itself; they are first shown in a short clip after the ending credits of episode 12 in Sora no Otoshimono: first season as they show their presence in front of Nymph, in episode 13 they were the ones responsible for the loss of Nymphs wings as they tore them off infront of Ikaros. They were outstandingly beaten as Ikaros summons the uranus system and overpowered their prometheus in firepower and size, thus sending them back to Synapse. As Sugata Eishirou repeatedly time travels from synapse it is without a doubt the patience of these harpies grow to insurmountable levels as they from time-to-time miss the opportunity in taking out Sugata's life.

History
They set a trap (by using Nymph's friendship with Ikaros to arrange a meeting) in a remote area by the mountains and by having Nymph conseal them behind one of her cloaking programs, plan to ambush Ikaros and make a fast return back to Synapse with their payload. When Ikaros responds to Nymph's request for a meeting and arrives at the ambush location, one of the Harpies takes aim with her powerful Prometheus cannon and fires a massive bolt of searing energy at the oblivious Ikaros, striking her with such impact that it vaporizes one of her wings and knocks her violently to the ground. Horrified by this cheap shot upon Ikaros and enraged when she learns their true intentions, Nymph turns upon the Harpies and fires her mighty "Paradise Song" energy beam at them in a surprise attack. Unfortunately, this attack only enrages the Harpies (who for the most part escaped the beam with only minor burns and singed feathers), as they proceed to brutally beat Nymph and painfully rip both of her wings out of her back. As they gang up on the helpless Nymph, Ikaros begins to awaken from being knocked out by the surprise Prometheus blast, and tries to get to her feet to aid her friend. The downfall of the Harpies begins when Ikaros goes to engage her Uranus Queen mode (to the horror of Nymph, who does not want Tomoki Sakurai to find out about the truth behind Ikaros and her past life). Tomoki accepts this somber truth and grants her permission to do whatever she needs to defeat the Harpies, and with that, she activates her Uranus Queen program. Realizing that the end is nigh, the Harpies fire away with their Prometheus cannons, but each shot is harmlessly deflected by Ikaro's powerful Aegis Shield, which makes her near immortal when it is deployed. Knowing that their fate has all but been sealed, the two Harpies try to escape, but are stopped when Ikaros summons the massive Hephestus spaceship that unleashes a massive blast of pure energy from it's gigantic cannons that is so powerful, the beam can be seen from space. The force of the energy blast sends the Harpies back to Synapse, where they face the wrath of their master for failing to complete their mission.

Forte Arc
Later on in the story, the Harpies make a return when they (on several occasions) unsuccessfully search the different levels of Synapse for Eishiro Sugata, who is there exploring the mysterious world of Synapse in the hopes of discovering the truth behind this new world. They fail to locate him most of the time, but on several of his trips to Synapse, they find him, but he escapes via the portal that Nymph's device opens between Earth and Synapse before they can capture him. It is only when Eishiro runs past them and meets the awakening Hiyori Kazane inside of the domed complex in Synapse that the Harpies (along with the Man of Synapse) capture him, but since he will soon forget everything about his current adventure due to the death of Hiyori's human avatar on Earth, they allow for him to escape when their master allows it. They both stay up in Synapse by their master's side, helping him in his plans for the creation of a new generation of Angeloids and other side tasks that he needs performed. Due to their failure on Earth when they faced Ikaros, they are not allowed to leave Synapse for the time being.